Mr Sims said service station chains were taking advantage of the general decline in the cost of fuel.

“When prices are down about 110c/L people are much less sensitive than when they are 150 or 160c/L,” Mr Sims said. “With prices coming down retailers might look to say ‘maybe we can just hang on to a bit more of this a little bit longer than we otherwise would’.”

The cost of turning oil into petrol has also soared — from 5.5c/L in 2004-05 to 13.5c/L, which is double the historical average. Encouragingly, the refiner margin had begun to shrink in recent weeks, Mr Sims said.

The ACCC is powerless to do anything about the refiner margin, which is a function of international demand for petrol. Demand remains high, despite the plunging price of oil.

The ACCC recently settled legal action it brought against much of the petrol retailing sector and a fuel-price information service, Informed Sources. As a result, the same raw data petrol retailers have been getting on each others’ prices will now be available to the ACCC, motoring groups and app developers.

The ACCC hopes this will lead to phone-based tools that show consumers the cheapest prices near them at any given moment. If more business goes to discounters there is a secondary benefit, because it puts pressure on others to lower their charges.

Mr Sims yesterday conceded the settlement had not addressed the original concern the ACCC had raised about “information sharing” between fuel sellers.